Crystal plasticity forming limit diagram analysis of rolled aluminum sheets

Abstract

Numerical simulations of forming limit diagrams (FLDs) are performed based on a rate-sensitive polycrystal plasticity model together with the Marciniak-Kuczynski (M-K) approach. Sheet necking is initiated from an initial imperfection in terms of a narrow band. The deformations inside and outside the band are assumed to be homogeneous, and conditions of compatibility and equilibrium are enforced across the band interfaces. Thus, the polycrystal model needs only to be applied to two polycrystalline aggregates, one inside and one outside the band. Each grain is modeled as an fcc crystal with 12 distinct slip systems. The response of an aggregate comprised of many grains is based on an elastic-viscoplastic Taylor-type polycrystal model. With this formulation, the effects of initial imperfection intensity and orientation, initial distribution of grain orientations, crystal elasticity, strain-rate sensitivity, single slip hardening, and latent hardening on the FLD can be assessed. The predicted FLDs are compared with experimental data for the following rolled aluminum alloy sheets: AA5754-

Effects of spatial grain orientation distribution and initial surface topography on sheet metal necking

“…Zhou and Neale, 1995;Wu et al, 1997 andInal et al, 2005). Using the M-K approach, the predicted FLDs based on crystal plasticity were in good agreement with measured FLDs for rolled metal sheet (Wu et al, 1998;Knockaert et al, 2002). However, the M-K approach needs the value of an artificial initial imperfection parameter f 0 , which cannot be directly measured by physical experiments.…”

On forming limit stress diagram analysis

“…Laukonis and Ghosh, 1978;Hosford, 1993, 1994;Zhao et al, 1996;Hiwatashi et al, 1998;Wu et al, 1998a;Kuroda and Tvergaard, 2000). There is no single curve in strain space that represents the forming limit, and this limits the use of conventional FLDs for assessing forming severity because the straining path of material elements in a real sheet metal forming process is usually not known with any certainty.…”

On crystal plasticity formability analysis for magnesium alloy sheets

“…Zhou and Neale, 1995;Wu et al, 1997;Inal et al, 2005;). Using the M-K approach, the predicted FLDs based on crystal plasticity were in good agreement with measured FLDs for rolled aluminum alloy sheets (Wu et al, 1998;Knockaert et al, 2002). However, almost all the FLD analyses have been for polycrystalline sheet metals with Face Centered Cubic (FCC) and Body Centered Cubic (BCC) crystallographic structures.…”